POTS, which Hayley suffered from for nine long months before she got the proper treatment, is difficult to diagnose because it is unusual and its symptoms -- stomach aches, nausea and vomiting, racing heart -- are common for a variety of other conditions, according to AOL's children's health specialist Dr. Jim Sears.
"It's pretty rare," Sears, a pediatrician who hosts "The Doctors," told AOL Health. "[Hayley's experience] is the typical story of someone who has vague symptoms. I'm not surprised that nobody could figure this out."
POTS affects the autonomic nervous system and causes a host of random, unpleasant side effects: fatigue, violent vomiting, intolerance to exercise, unquenchable thirst and tachycardia, or rapid heartbeat. Only about 1 percent of all teenagers are diagnosed with the syndrome, two-thirds of them girls, and about 80 percent of those who do have it are female, most of them of child-bearing age.